Host rewrites

Replace the host header value before forwarding a request to a backend service by using the URLRewrite filter.

For more information, see the Kubernetes Gateway API documentation.

Before you begin

  1. Follow the Get started guide to install kgateway.

  2. Follow the Sample app guide to create a gateway proxy with an HTTP listener and deploy the httpbin sample app.

  3. Get the external address of the gateway and save it in an environment variable. 

    export INGRESS_GW_ADDRESS=$(kubectl get svc -n kgateway-system http -o jsonpath="{.status.loadBalancer.ingress[0]['hostname','ip']}")
echo $INGRESS_GW_ADDRESS  
    kubectl port-forward deployment/http -n kgateway-system 8080:8080

In-cluster service host rewrites

  1. Create an HTTPRoute resource for the httpbin app that uses the URLRewrite filter to rewrite the hostname of th request. In this example, all incoming requests on the rewrite.example domain are rewritten to the www.example.com host.

    kubectl apply -f- <<EOF
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: httpbin-rewrite
  namespace: httpbin
spec:
  parentRefs:
  - name: http
    namespace: kgateway-system
  hostnames:
    - rewrite.example
  rules:
     - filters:
       - type: URLRewrite
         urlRewrite:
           hostname: "www.example.com"
       backendRefs:
        - name: httpbin
          port: 8000
EOF
    Setting Description
    spec.parentRefs The name and namespace of the Gateway that serves this HTTPRoute. In this example, you use the http gateway that was created as part of the get started guide.
    spec.rules.filters.type The type of filter that you want to apply to incoming requests. In this example, the URLRewrite filter is used.
    spec.rules.filters.urlRewrite.hostname The hostname that you want to rewrite requests to.
    spec.rules.backendRefs The backend destination you want to forward traffic to. In this example, all traffic is forwarded to the httpbin app that you set up as part of the get started guide.

  2. Send a request to the httpbin app on the rewrite.example domain. Verify that you get back a 200 HTTP response code and that you see the Host: www.example.com header in your response.

    ℹ️
    The following request returns a 200 HTTP response code, because you set up an HTTPRoute for the httpbin app on the www.example.com domain as part of the getting started guide. If you chose a different domain for your example, make sure that you have an HTTPRoute that can be reached under the host you want to rewrite to.
    curl -vi http://$INGRESS_GW_ADDRESS:8080/headers -H "host: rewrite.example:8080"
    curl -vi localhost:8080/headers -H "host: rewrite.example"

    Example output:

    ...
{
 "headers": {
   "Accept": [
     "*/*"
   ],
   "Host": [
     "www.example.com"
   ],
   "User-Agent": [
     "curl/7.77.0"
   ],
   "X-Envoy-Expected-Rq-Timeout-Ms": [
     "15000"
   ],
   "X-Forwarded-Proto": [
     "http"
   ],
   "X-Request-Id": [
     "ffc55a3e-60ae-4c90-9a5c-62c8a1ba1076"
   ]
 }
}

External service host rewrites

  1. Create a Backend that represents your external service. The following example creates a Backend for the httpbin.org domain.

    kubectl apply -f- <<EOF
apiVersion: gateway.kgateway.dev/v1alpha1
kind: Backend
metadata:
  name: httpbin
  namespace: default
spec:
  type: Static
  static:
    hosts:
      - host: httpbin.org
        port: 80
EOF

  2. Create an HTTPRoute resource that matches incoming traffic on the external-rewrite.example domain and forwards traffic to the Backend that you created. Because the Backend expects a different domain, you use the URLRewrite filter to rewrite the hostname from external-rewrite.example to httpbin.org.

    kubectl apply -f- <<EOF
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: backend-rewrite
  namespace: default
spec:
  parentRefs:
  - name: http
    namespace: kgateway-system
  hostnames:
    - external-rewrite.example
  rules:
     - filters:
       - type: URLRewrite
         urlRewrite:
           hostname: "httpbin.org"
       backendRefs:
       - name: httpbin
         kind: Backend
         group: gateway.kgateway.dev
EOF

  3. Send a request to the external-rewrite.example domain. Verify that you get back a 200 HTTP response code and that you see the Host: httpbin.org header in your response.

    curl -vi http://$INGRESS_GW_ADDRESS:8080/headers -H "host: external-rewrite.example:8080"
    curl -vi localhost:8080/headers -H "host: external-rewrite.example"

    Example output:

    * Request completely sent off
< HTTP/1.1 200 OK
HTTP/1.1 200 OK
< content-type: application/json
content-type: application/json
< content-length: 268
content-length: 268
< server: envoy
server: envoy
< access-control-allow-origin: *
access-control-allow-origin: *
< access-control-allow-credentials: true
access-control-allow-credentials: true
< x-envoy-upstream-service-time: 2416
x-envoy-upstream-service-time: 2416
< 

{
  "headers": {
    "Accept": "*/*", 
    "Host": "httpbin.org", 
    "User-Agent": "curl/8.7.1", 
    "X-Amzn-Trace-Id": "Root=1-6859932a-1fb1dc706dadcc183b407d4d", 
    "X-Envoy-Expected-Rq-Timeout-Ms": "15000", 
   "X-Envoy-External-Address": "10.0.15.215"
  }
}

Cleanup

You can remove the resources that you created in this guide. 
kubectl delete httproute httpbin-rewrite -n httpbin
kubectl delete httproute backend-rewrite 
kubectl delete backend httpbin
Path rewrites